The role of calcium, cyclic GMP and cyclic AMP in the regulation of hydrolase secretion from the rat exocrine pancreas will be explored on tissue fragments, isolated acinar cells and purified plasma membranes. Specific binding of gastrointestinal hormones (such as pancreozymin, secretin, vasoactive intestinal polypeptide, bovine pancreatic polypeptide, and bombesin) will be examined, together with the activity of a guanyl nucleotide regulatory site and of membrane-bound adenylate cyclase. Guanylate cyclase, cyclic nucleotide phosphodiesterases (and their calcium-dependent activator), the RC yields (reversibly) R plus C equilibrium of cyclic AMP and cyclic GMP dependent-protein kinases, and the "phospholipid effect" will also be explored, after treatment with gastrointestinal hormones, muscarcinic neurotransmitters and ionophore A-23187. In addition, the effects of cholera toxin and the properties of Ca-ATPase in pancreatic plasma membrane will be documented. Accessorily, the mode of action of pancreatic hydrolases will be investigated, such as the interaction of pancreatic lipase with triglycerides, in the presence of colipase and bile salts. BIBLIOGRAPHIC REFERENCES: In vitro and in vivo effects of bombesin and bombesin-like peptides on the rat pancreas. Mechanism of action. in "Hormonal Receptors in Digestive Tract Physiology". S. Bonfils, P. Fromageot and G. Rosselin Eds. North-Holland, Amsterdam 247-260, 1977. J. Christophe, M. Deschodt-Lanckman, M. Adler and P. Robberecht. Initial steps in the action of cholecystokinin and cholinergic agents of pancreatic acinar cells. in "Hormonal Receptors in Digestive Tract Physiology" S. Bonfils, P. Fromageot and G. Rosselin Eds. North-Holland, Amsterdam 237-246, 1977. J.D. Gardner, J.P. Christophe, T.P. Conlon and E.K. Frandsen.